Ecological Orbits: How Planets Move and Populations Grow

Article excerpt

Ecological Orbits: How Planets Move and Populations Grow, L. Ginzburg and M. Colyvan, Oxford University Press: Oxford, 2004.

Population ecology comprises a small set of standard models and most new models are just minor variations on long-held ideas. Therefore, it would be natural not to expect a great deal of innovation from a new book. On the contrary, Ecological Orbits presents a fresh and stimulating perspective. The authors, ecologist Lev Ginzburg and philosopher Mark Colyvan, ask the reader to sit back and reflect on the basic concepts that make population ecology what it is. Some modifications, they suggest, could influence the way that we think about the processes of population growth in important ways. Though it is notably lacking in mathematical formulas, this book is a contribution to theoretical ecology. It is theoretical in the more basic sense, encouraging us to revisit our basic concepts and notions about what populations are and how they work and the implications that these concepts have for how we conduct our science. What's more, the tone of Ecological Orbits is disarming and engaging. It could well be used in an undergraduate ecology class or as recommended reading for non-scientists interested in our discipline. Above all, it is a pleasure to read.

The reference to planets in the title is the first hint that this is not a conventional introduction to population ecology. Why planets? Ginzburg and Colyvan believe that populations moving through a state space, like massive bodies moving in physical space, have inertia. Thus, the authors take their dynamical cues from celestial mechanics. This is not the only recent book to find deep similarities between population biology and physics: Peter Turchin's Complex Population Dynamics (2003, Princeton University Press) takes this approach as well. What is there to recommend this mechanical-biological approach to population growth? The answer to this question, as to all scientific questions, ultimately is an empirical one. However, Ginzburg and Colyvan are willing to bet that the analogy between population growth and classical mechanics goes at least deep enough to suggest that it is changes in birth and death rates and subsequent changes in the population growth rate-that is accelerations-that should be the focus of population ecology, rather than changes in population size. They believe, moreover, that many recent developments in theoretical ecology have missed the point by focusing on all the minor details of population fluctuations. As a result, many ecological models are over-fit and too highly parameterized (cf., Ginzburg and Jensen, 2004. Trends Ecology Evolution, 19:121-126). The solution they propose is to get back to the basics of ecological theory: to use what we know about allometry, to find theories that explain what we don't see in population cycles (namely, periods of between two and six generations) and to focus on three basic forces that cause population accelerations-energetics, maternal effects and predator-prey interactions. This is a reasonable blueprint for a research program and much of the remainder of the book is dedicated to demonstrating what this research program will look like.

Before this, however, there is a brief philosophical interlude (chapter two) to engage the current debate over whether or not ecologists have discovered any general laws. In my own view, the dispute itself is misguided, and the discussion here is likewise a bit tiresome. Scientific laws, like other laws, are not deep mystical properties of the universe. …